Electric accumulator



M. WILDERMAN ELECTRIC ACCUMULATOR Filed Oct. 31, 1929 Jan. 19, 1932.

INVENTOR Wa, A 2%.

Patented l Jan. 19, 1932 i PATENT OFFICE ELECTRIC ACCUMULATORApplication ledctober 3l', 1929. S'erial No. 403,898.

This invention relates to an electric accumulator and provides materialimprovements tion,

vlo

is on the regulates 1n the efficiency and utility thereof.

This application is a continuation in part of` my application Seria-1No. 745,637, filed October 24, 1924.

The usual electric accumulator comprises spaced electrodes immersed in asolution of sulphuric acid. All chemical react-ions in the accumulatortake place at the surface of conjtact between the sulphuric acid and thesolid sponge lea-d and lead peroxide, as well as with the solid SOiPbwhich separates on the elecl trodes. During discharge of the battery theacid becomes more dilute and during charge more concentrated. The acidwhich surface of contact is the first to take partin the reaction sothat during charge or discharge there is a condition of non-uniform aciddensity existing in the cell.\

becomes During discharge the more 'concentrated acid between theelectrodes is supplied by diffusion tothe more dilute acid at thesurface of contact with the electrodes, and in the pores of theactivematerial. In charging, the reverse condition exists, the moreconcentrated acid lying adjacent the electrodes and inthe pores of theactive material, Diffusion is relatively a slow process and it cannotsupply or remove the HZSO, to or from the electrodes with the same speedas it is removed by the current from thesoluor is increased in the sameat'the surface of the electrodes and within the pores of the activematerial. Asa result of this', the voltage, and with it the ampere-hourand watt#l hour capacity drop considerably on account Y of the drop ofacid concentration at theclectrodes during discharge, this drop beingthe greater the higher the current of discharge.

During charging the rate of diffusion again the rate of transportationof the HZSO.1 from the acid Within the pores and the surface of theelectrodes to the acid layer therebetween so long as no gassing takesplace in the cell. At 2.3 volts the cell begins to gas, separatinghydrogen and oxygen which effectively stir the acid solution between thediaphragm and the electrodes making the density of the solution uniform.The

cumulator depends, including its speed of recuperation, canonly-be'obtained, if the speed with which the vsulphuric acid of thetotal acid solution in the battery is brought to the surfaces oftheelectrodes is made to be greater than itis under. the action ofdiffusion.

vThis I achieve by the introduction of automatic' circulation of thesolution between the electrodes under the action of charge anddischarge.

I provide means whereby the hydrostatic and electro-osmotic pressuresare employed for producing effective and automatic circulation andmixing of the electrolyte between the electrodesv so as to prevent thesetting up ofthe conditions above described. To this end I employ adiaphragm having a rate of percolation materially greater than thewooden separators or threaded rubber separators now employed. Ipreferably employ a separator made of porous ebonite. These separatorsmay be readily manufactured and their properties may be very accuratelycontrolled. Their process of manufacture is fully set forth in my PatentNo. 1,651,567 for process of manufacturing porous bodies, diahragms,filters and the like of-ebonite, dated ecember 6th, 1927.'

In order to 'fully enjoy the advantages of my inventlon a `number ofconditions must be complied with, as follow a A diaphragm must be usedas a separator in order that hydrostatic and electroosmotic pressuresare created between the electrodes. 'lhis condition is not obtained byperforated sheets since no electro-osmotic they are used.

b The concentration of the electrolyte on the different sides of thediaphragm must be maintained of a different strength during lo' i chargeand discharge as otherwise no hydrostatic pressure is obtainable, andthe electroosmotlc pressure is materially diminished. In order tomaintain this difference in concentration of electrolyte I so positionthe diaphragm that a greater quantity of electrolyte lies on one side ofthe plate than on the other. Preferably the diaphragm is placed so thatit is closer to the negative electrode than to i and the electrodes arevery small, usually one millimeter or less, the separators must be soconstructed and be of such properties that the proper positioning of thediaphragm is maintained throughout the life of the battery. For thisreason I provide the separators or diaphragms with a non-compressibleframe or ribs capable of effectively counteracting the bending andbuckling o the electrodes, the frame or ribs and the diaphrgm at thesame time remaining unaffected by the electrode or by the gases evolvedin the battery.

d While the separator should be placed closer to the negative than tothe positive electrode, it is desirable to leave a free space at thenegative side of the diaphragm between the diaphragm and the negativeelectrode so as to permit of circulation of the solution be- `as that ofthe earthenware tween the diaphragm and the electrode.

e The diaphragm must have a very high rate of percolation in order thatthe small values of the hydrostatic pressure and of the electro-osmoticpressure is suilicient for producing the desired results.

The speed of percolation of a porous diaphragm'depends upon the porosityand upon the radius of the capillarities in the diaphragm and only agreat porosity and a suficient radius ofthe capillaries makes itpossible to secure the desired speeds of percolation. By makingseparators as described in my patent above referred to, itis possible tosecure diaphragms having remarkably high rates of percolation. Forexample, careful investigations extending over long periods and madewith numerous samples, have shown that the speed of percolation throughan ebonite diaphragm made of a powder of grain 0.9 millimeters and ofabout 50% porosity is from 40,000 to 100,000 times as great as that ofWooden diaphragms of the same thickness, about v8000 times as greatdiaphragms used in Leclanch cells and about 1000 times as w great asthat of threaded rubber after the lsolution is on percolation of tlatter have been in water or solution for a,

few days.

The above was established by direct measurements of the speed ofpercolation by the method of P. A. Guye, Journal de Chimie et dePhysique, Vol. II, page 79 (1904) With a treated wooden separator 0.9millimeter thick, about 20 cm2 surface, 0.14 cm3 passed per minute underthe pressure of a column of solution 107 cm high, i. e. 0.000007 cm3solution passed per cm2 of separator per minute and 1 mm pressure ofsolution.

With porous ebonite separators of the same dimensions 0.35 to 0.7 cm3 ofsolution passed per cm2 of the diaphragm per minute and 1 mm pressure ofthe solution.

The last can also be much simpler illustrated by bringing a drop ofwater on a porous ebonite separator; it passes instantaneously to theother side also when the thickness of the drop became 0.1 mm or evenless.

The .thickness of the separators being usually about 0.9 or 1 mm theabove data give also the exact amounts of solution which must pass thediaphragm, whenit is placed between the electrodes and an overpressureof 1 mm water alone exists, for one reason or another, from one side ofthe diaphragm to the other. If the distance between the diaphragm andthe electrode be 1 mm the total vamount of solution per centimetersquare of the diaphragm between the electrode and the separator is 0.1cm3, that is, the solution between the separator and the electrode hasbeen renovated 3, 5 to 7 times per minute, and if this distance is only0.4 mm the solution between the diaphragm and the electrode has beenrenovated 9 to 18 times per minute. The pressure on the solution in anygiven capillary of the diaphragm being greater at the one end of thecapillary than at the other, the same is bound to move in the capillaryfrom the side of greater pressure to the side of the smaller pressure.ccording to the elementary laws of hydrostatics the total pressure onthe solution in any such capillary of the diaphragm is at each end equalto the section of the capillary multiplied by the height of the columnof the solutionfrom the capillary to the top surface of the solution inthe cell multiplied by the average specific gravity of this column. Iftherefore for one reason or'another the specific gravities or theconcentration of the both sides of the diaphragm different such amovement of the solution through the dia hragm is 4 inevitable howeverthe cell may constructed, whether the separators and the electrodes areclosed up in the cell or not, the amount of solution passing through thediaphragm depending besides the ove ressure upon the speed of ediaphragm. It is very great in case of a orous ebonite separator, andextremely sma l or practically zero for all practical purposes in caseof a wooden separator. A

In the porous separator of great percola.

tion'the solution moving through the diaf phragm is doing this at thetotal surface of the electrode, not on one or two places of theelectrode alone; and the distance between the two electrodes, as well asbetween the separator and the electrodes, being very small `a very smallmovement of the solution is sulicient to bring it mechanically up to thesurfaces of the electrodes themselves. It is for this reason that Idesignate this as circulation of the .electrolyte between theelectrodes, extending its activity up to the surfaces of the electrodesthemselves where it is most needed.

To create such a difference of the concentration on both sides of thediaphragm in an automatic manner I place the diaphragm between theelectrodes in such a manner that more solution is between the diaphragmand one of the electrodes than between the same asd the other. Theobject being to keep the concentration of the thicker layer of solutionbetween the diaphragm and the electrode higher, when during dischargethe same number of molecules of sulphuric acid disappear at eachelectrode.

If the separator is so placed between the electrodes that the amount ofsolution on each side ofthe separator is the same, the concentration ofthe solution during discharge will be on each side of it also the sameand there will be no, or practically no, movement of the solutionthrough the diaphragm, also when its speed of percolation is otherwisegreat. Similarly if the separator is placed with the one side straighton one of the electrodes (say the negative), so that no free spacebetween the separator and the electrode is left, the circulation ismechanically prevented because the requisite free space for movement ofthe solution is not provided for. For this reason the separator must beso placed between the electrodes that there should be free space betweenthe separator and each of them.

In a cell of a A. H. capacity, having 11 electrodes and 10 separators ofsay 13 cm X 15 cm, the total surface of the separator is about 2000 cm2and the total surface of the capillaries of the separators having a 50%porosity through which the` solution is pressed is about 1000 cm2, whichfor a separator of greatspeed of percolation is enormous.

In the accompanying drawings given by way of example to illustrate thepresent invention,

Figure 'l is a separator,

Figure 2 is a plan view of a. slightly modified form of separator,

' Figure 3 is a cross ysection of the frame of plan view of one form ofthe separator on line III-III, if the frame is madeV of a nonporoussubstance such as ebonite,

Figure 4 is the cross section of tbe separator on line IV-IV, when theframe and the vertical strips are made of a nonporous substance such asnonporous ebonite, while the diaphragm consists of a porous substancesuch as porous ebonite,

Figure 5 gives the cross section of the same separator on the same lineIV-IV of the frame, the vertical strips also consist of a poroussubstance such as porous ebonite.

Figure 6 is a horizontal section of a cell showlng the arrangements ofthe electrodes and thev separators between so placed as to give moresolution at the positive electrodes than at the negative electrodes, v

Figure 7 is a vertical section of the same battery viewed from thenarrow side of the battery on the line VII-VII .of Figure 6,

F ioure 8 gives a cross section of a separator Fig. 2 made wholly of aporous substance such as porous ebonite containing two vertical stripsat the ends and small vertical strips between at eachside of theseparator.

Referring to the drawings, the separator illustrated in Figures l, 3,4,6 and 7 comprises a web portion 2 of say porous ebonite which islcompletely surrounded by a frame 3 of nonporous ebonite. The web 2 isprovided with spaced ribs 4 which contact with adjacent electrodes tomaintain the separator spaced therefrom the web 2 being more reV movedfrom one electrode (in this case from the positive electrode) than fromthe other (in this case the negative electrode), the front surfaces ofthe frame and of the ribs being removed from the web more on one sidethan on the other (see cross section Figures 3, 4, as well as Figures 6and 7). The top portion '5 and the bottom portion 6 of the frame 3' areprovided with projections 7 which allow the gas to escape during 'chargeof the cell. i

'Figure 5 shows the same Figure 4 if the separator is wholly made ofporous ebonite` the front surfaces ofthe frame and of its projections 7in the top and the vertica-l ribs 4 being more removed from the Surfaceof the web 2 on one side than on the other.

In the modified form of separator shown in Figure 2 and Figure 8, thewide ribs 3 andthe narrow ribs 4 as well as the web 2- are made of aporous substance such as ebonite. The ribs 4 and the vertical ribs 3extending beyond the plane of the web on both sides, more on the oneside than on the other, the separators being used with the electrodes inthe battery and arranged in the same manand bottom portion ner asillustrated in Figures 6 and 7 g In this case the separator is showntocontain also ribs 8 between the ribs 4 on one side of the 9 asillustrated in fFigures 6 and 7. The frames 3 and the vertical ribscontactin with the adjacent electrodes prevent distortion of theelectrodes which have a tendency to warp or buckle, especially at highrates of discharge. In Figure 7 the level of the electrolyte isindicated by the line lil-E. The cell is provided with a vent plug 10which allows the gases developed inthe cell to escape.

In the embodiment shown in Figures 1, 3, 4, 5, 6, and 7 the frame 3extends completely around the separator. --c

It should be understood that the present invention is not restrictedtothe forms of separator given by way of illustration here, nor to thekind of material used for the porous separator, as long as the porousseparator is of a great speed of percolation and the separator when usedin connection with the electrodes .in the battery is removed from theactive material of the one electrode more than from that of the other.

I claim: l. In an electric accumulator having spaced electrodes adaptedvto be submerged in an electrolyte, a porous diaphragm having a j web,the diaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, the diaphragm contacting with theadjacent electrodes, the web of the diaphragm being more removed fromone electrode than from the other and forming unequal free spaces oneach side of the web for free circulation of the electrolyte.

2. In an electric accumulator having spaced electrodes adapted to besubmerged in an electrolyte, a porous ebonite diaphragm having a web,the diaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, the diaphragm contacting with theadjacent electrodes, the web of the diaphragm being more removed fromone electrode than from the other and forming unequal free spaces oneach side of the web for free circulation of the electrolyte.

3. In an electric accumulator having spaced electrodes adapted to besubmerged .in an electrolyte, a porous diaphragm having a web, thediaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, the diaphragm contacting with theadjacent electrodes, the web of the diaphragm being more removed fromone electrode ythan from the other and forming unequal free spaces oneach side of the web for free circulation of the electrolyte, thediaphragm having ribs which roject belyond the web more on one of itssiv es than on the-other..

4. In Van electric accumulator havin spacedelectrodes adapted to besubmerge in an electrolyte, a porous ebonite diaphragm having a web, thedia hragm'being of great f5 speed of percolation, ying betweentheelectrodes and Aacting as a separator, the diaphra contacting with theadjacent electrodes, the web of the diaphragm being more removed fromone electrode than from the other and forming unequal free spaces oneach side o the web for free circulation of the electrolyte, thediaphragm having ribs which project beyond the web more on one of itssides than on the other.

5. In an electric accumulator havin spaced electrodes adapted to besubmerged in an electrolyte, a porous diaphragm having a web, thediaphragm being of great speed of percolation,'lying between theelectrodes and acting as a separator, the diaphragm contacting with theadjacent electrodes, the web of the diaphragm being more removed fromone electrode than from the other and forming unequal free spaces oneach side of the web for free circulation of the electrolyte, the webbeing surrounded by a frame which is thicker than the web and projectsbeyond the surface of the web on both sides, the projection on one sidebeing greater than on the other.

6. In an electric accumulator having spaced electrodes adapted to besubmerged in an electrolyte, a porous ebonite diaphragm having a web,the diaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, the diaphragm contacting with theadjacent electrodes, the web of the diaphragm being more removed fromone electrode than from the other one and forming unequal free spaces oneach side of the web for free circulation of the electrolyte, the' webbeing surrounded by a frame which is thicker than the web and projectsbeyond the surface of the web on both sides, the projection on one sidebeing greater than on the other.

7. In an electric accumulator having spaced lelectrodes adapted to besubmerged in au electrolyte, a porous diaphragm having a web, thediaphragm being of great speed of percolation, lying between theelectrodes and acting' as a separator, the diaphragm contacting with thead]acent electrodes, the web of the diaphragm being more removed theother and forming unequal free spaces on\elzich side of the web for freecirculation of t e electrolyte, the web being surrounded by a framewhich is thicker than the web and projects beyond the surface of the webon both sides, the projection on one side being greater than on theother, and other ribs within the frame and of the same thickness as theframe.

8. In an electric accumulator havin spaced electrodesadapted to besubmerge in an electrolyte, a porous ebonite diaphragm having a web, thediaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, the diafrom one electrode thanfrom phragin contacting with the adjacent electrodes, the web of thediaphragm being more removed from one electrode than from the other andforming unequal free spaces on each side of the web for free circulationof the electrolyte, the web being surrounded by a frame which is thickerthan the web and projects beyond the'surface of the web. on both sides,the projection on one side being greater than on the other, and otherribs within the frame and of the same thickness as the frame.

9. In an electric accumulator having spaced electrodes adapted to besubmerged in an electrolyte, a porous diaphragm having a web, thediaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, vthe diaphragm contacting with theadjacent electrodes, the web of the' diaphragm being more'V removed fromone electrode than from the other and forming unequal free spaces oneach side of the web for free circulation of the electrolyte, thediaphragm having nonporous ribs projecting beyond thelsurface of the webon both sides, the projection on one side being greater than on theother.

10. In an electric` accumula-tor having spaced electrodes adapted to besubmerged in an electrolyte, a porous ebonite diaphragm having a web,the diaphragm being of great speed of percolation, lying between theelectrodes and acting as a separator, the diaphragm contacting with theadjacent elecf-rodes, the web of the diaphragm being more removed .fromone electrode than from the other and forming unequal free spaces on Yeach side of the web for free circulation of the electrolyte, thediaphragm having ribs of non-porous ebonite projecting beyond thesurface of the web on both sides, the projection on one side beinggreater than on the other. A 11. In an electric accumulator havin-gspaced electrodes adapted to be submerged in an electrolyte. a porousdiaphragm having a web, the diaphragm being of great Speed ofpercolation, lying between the electrodes and acting as a separator, thdia-v phragm contacting with the adjacent electrodes, the web of thediaphragm being more removed from one electrode than from the other andforming unequal free Aspaces on each side of the web for freecirculationo the electrolyte, the web being surrounded by a frame whichis thicker than the web and projects beyond the surface of the web onboth sides, the projection on one side being greater than on the other,at least one of the horizontal portions of the frame being provided withchannels for the escape of gas;

speed of percolation, lying between the electrodes and acting as aseparator, the diaphragm contacting with the adjacent electrodes, theweb of the diaphragm being more removed from one electrode than from theother and forming unequal free spaces on each side of the web for freecirculation of the electrolyte, the web being surrounded by a framewhich is thicker than the web and projects beyond the surface of the webon both sides, the projection on one side being greater than on theother, at least one of the horizontal portions of the frame being prol`vided with channels for the .escape of gas.

In testimony ywhereof I have hereunto set my hand.

ME YER VVILDERMAN.

12. In an electric accumulator having I

